UNDERSTANDING HOLOCENE FIRE-VEGETATION LINKAGES AND THE ROLE OF HUMANS AND CLIMATE

Fire history is an essential part of Earth system science, but that recognition was not the case in the early 1970s when Herb Wright and Bud Heinselman described the fire history of the Boundary Waters Canoe Area. Subsequent paleofire studies in the U.S., led by students of Wright, highlighted the importance of long-term fire information for understanding modern vegetation dynamics. Recent advances in paleofire research have built on this legacy by providing more precise approaches for fire-history reconstructions and clarifying the links between long-term variations in fire and climate. A paradox remains in fire-history research: At the regional to global scale, the primary driver of fire activity is climate, whereas at local scales, prehistoric humans are known to have shaped vegetation by altering ignitions and fuels. What occurs at intermediate spatial scales where humans and climate interact to shape landscape history?

The fire history of temperate forests ecosystems is germane for understanding fire-climate-human linkages: In the western U.S., paleoecologic records suggest that Holocene climate variations maintain fires in conifer forests; pre-EuroAmerican fires were localized. Similarly in Patagonia, past fires were strongly influenced by changes in the seasonal cycle of insolation, the strength of the westerlies and interannual/interdecadal climate variability. In contrast, in central Europe, humans have been the dominant driver of fires since the Neolithic period and in New Zealand, wildland fires were rare prior to the arrival of Maori ~700 years ago. Deliberate burning by early people led to loss of native forest and expansion of open landscapes. Tasmania shows both human and climate influences at the landscape scale; humans were long-term ignitions sources but one or more large drought-driven fires in the late Holocene led to a decline of subalpine forest. In summary, human and climate drivers converge to shape prehistoric fire regimes at the landscape to subregional scale, but the feedbacks are complex and context-specific. Herb Wright early on recognized the value of paleofire information for understanding modern ecosystems, and the extent to which past climate and human activity have shaped present landscapes remains an area of active scientific and conservation interest.